There is known a semiconductor package in which a semiconductor chip (semiconductor element) is covered (encapsulated) with a resin-made encapsulating material. The encapsulating material for the semiconductor chip is produced by molding a resin composition through, e.g., a transfer molding method. In such a method, in the case where the resin composition is not sufficiently degassed, there is a problem in that voids are formed in the encapsulating material.
As one method for preventing formation of the voids in the encapsulating material, patent document 1 discloses a method for degassing the resin composition. In the method, a bent port (degassing chamber) for decompression is provided in the middle of a double-axis type kneading extruder so as to be communicated with an inside thereof. By decompressing the inside of the bent port, the resin material is degassed.
However, according to the one method of the patent document 1, if a pressure in the bent port is too low, a material contained in the double-axis type kneading extruder is sucked toward the bent port. For this reason, the pressure in the bent port cannot be sufficiently lowered. This makes it impossible to sufficiently degas the material. As a result, when the semiconductor chip is sealed with the produced resin composition, there is a possibility that the voids are formed in, the produced resin composition.
Further, another method in that the degassing chamber is provided between two double-axis type kneading extruders is also proposed. In this method, an inlet port of the degassing chamber is connected to a discharge passage of a first kneading apparatus, and an outlet port of the degassing chamber is connected to a charge passage of a second kneading apparatus. A material kneaded in the first kneading apparatus is degassed in the degassing chamber and then is kneaded in the second kneading apparatus. In this regard, a decompression of the degassing chamber is enabled by sealing a side of the inlet port of the degassing chamber with the material contained in the first kneading apparatus and a side of the outlet port of the degassing chamber with the material contained in the second kneading apparatus.
However, according to another method, when the degassing chamber is decompressed, the material contained in the second kneading apparatus is sucked toward an opposite direction with respect to a direction to which the material contained in the second kneaded apparatus is to be transferred, which results in poor stability.    Patent Document 1: JP-A 2001-81284.
It is an object of the present invention to provide a degassing apparatus which can easily and reliably degas a kneaded material.
In order to achieve the object, one aspect of the present invention is directed to a degassing apparatus comprising: a housing having an inlet port from which a material that has been kneaded is introduced, a degassing chamber in which the kneaded material is degassed and an outlet port from which the kneaded material that has been degassed, is discharged; a decompression device that decompresses the degassing chamber; and a separating device that hermetically separates the outlet port from the degassing chamber, wherein in a state that the outlet port is hermetically separated from the degassing chamber by the separating device, and then the degassing chamber is decompressed by the decompression device, the material introduced into the degassing chamber is degassed.
In the degassing apparatus of the present invention, it is preferred that the housing further has a cylindrical portion which is formed into cylindrical shape and provided between the inlet port and the outlet port, the separating device is rotatably provided in the cylindrical portion and has a rotor having plural partitioning plates which partition an inside of the cylindrical portion into plural spaces, and the material is delivered to the outlet port with the partitioning plates by rotation of the rotor.
In the degassing apparatus of the present invention, it is preferred that the degassing chamber is provided between the inlet port and the cylindrical portion.
In the degassing apparatus of the present invention, it is preferred that the decompression device has a conduit line which communicates with the degassing chamber and the degassing chamber has the plural spaces of the cylindrical portion, and each of the plural spaces is allowed to be rotated by the rotation of the rotor, and one space of the plural spaces, which communicates with the conduit line, is decompressed through the conduit line.
In the degassing apparatus of the present invention, it is preferred that the degassing apparatus has a non-communicating state in which the one space does not communicate with the inlet port and the outlet port, and the material in the degassing chamber is degassed in the non-communicating state.
In the degassing apparatus of the present invention, it is preferred that a gap is formed between an inner peripheral surface of the cylindrical portion and a distal end portion of the partition plate and a width of the gap is set to be equal to or less than 0.2 mm.
In the degassing apparatus of the present invention, it is preferred that at least a surface of the rotor is constituted of a nonmetallic material.
In the degassing apparatus of the present invention, it is preferred that at least an inner peripheral surface of the cylindrical portion is constituted of a nonmetallic material.
In the degassing apparatus of the present invention, it is preferred that a retention time of the material in the degassing apparatus is equal to or less than 1 minute.
In the degassing apparatus of the present invention, it is preferred that when the degassing chamber is decompressed by the decompressing device, the pressure in the degassing chamber is set to be equal to or less than 60 kPa.
In the degassing apparatus of the present invention, it is preferred that the inlet port is connected to a discharge passage of a kneading device in which the material is kneaded.